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Unit 2: MatterUnit 2: Matter
Properties and ChangesProperties and Changes
CHEMISTRYCHEMISTRY
August 29, 2007August 29, 2007
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BrainteaserBrainteaser�� Define physical and chemical change Define physical and chemical change
(in your own words).(in your own words).
�� Is this picture of a physical or a Is this picture of a physical or a
chemical change?chemical change?
––Explain yourExplain your
reasoningreasoning
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Properties of Matter—Substances
• Matter that has a uniform and unchangingcomposition is called a substance, also known as a pure substance.
• For example:
– Table salt
– Water
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� Why is seawater NOT an example of a substance?
� Seawater, on the other hand, is not a substance because samples taken from different locations will probably have differing compositions.
– That is, they will contain differing amounts of water, salts, and other dissolved substances.
Properties of Matter—Substances
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Physical Properties of Matter
• A physical property is a characteristic that can be observed or measured withoutchanging the sample’s composition. Physical properties describe pure substances, too.
NOT IN NOTES… SORRY
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Physical Properties & ChangesPhysical Properties & Changes
�� Characteristics of a substance that Characteristics of a substance that
can be observed without altering the can be observed without altering the
identity of the substance.identity of the substance.
–– StateState, , densitydensity, color, , color, odorodor, melting , melting
point, point, boiling pointboiling point, luster, conductivity, , luster, conductivity,
brittlenessbrittleness, malleability, malleability. .
NOT IN NOTES… SORRY
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Physical ChangePhysical Change
�� Does not Does not alteralter the identity of a substancethe identity of a substance
–– Crushing, tearing, changes of state (solid to Crushing, tearing, changes of state (solid to
liquid to gas)liquid to gas)
NOT IN NOTES… SORRY
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Extensive and Intensive Properties
• Physical properties can be further described as being one of two types.
– Extensive properties are dependentupon the amount of substance present.• For example, mass, which depends on the amount of substance there is, is an extensive property.
• Length and volume are also extensive properties.
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Extensive and Intensive Properties
• Intensive properties are independentof the amount of substance present.
– Density is an example of an intensive property of matter.
• Density of a substance (at constant temperature and pressure) is the same no matter how much substance is present.
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Chemical Properties of Matter
• Chemical property : The ability of a substance to combine with or change into one or more other substances.
– Rusting is an example of a chemical property of iron
• Similarly, the inability of a substance into change into another substance is also a chemical property.
– Resistance of iron to undergo change in the presence of nitrogen.
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Chemical ChangesChemical Changes
�� Characteristics of a substance that cannot Characteristics of a substance that cannot
be be observedobserved without altering the identity of without altering the identity of
the substance.the substance.
–– ReactivityReactivity, flammability, reaction types, flammability, reaction types
�� Alter the identity or chemistry of substanceAlter the identity or chemistry of substance
–– Burning, cooking, rustingBurning, cooking, rusting
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States of MatterStates of Matter
• The physical state of a substance is a physical property of that substance.
• Each of the three common states of matter can be distinguished by the way it fills a container.
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SolidsSolids
• A solid is a form of matter that has its own definite shape and volume.
–For example: Wood, iron, paper, and sugar
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SolidsSolids
• The particles of matter in a solid are very tightly packed; when heated, a solid expands, but only slightly.
• Because its shape is definite, a solid may not conform to the shape of the container in which it is placed.
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LiquidsLiquids
• A liquid is a form of matter that flows, has constant volume, and takes the shape of its container.
– Examples: Water, blood, mercury
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LiquidsLiquids• The particles in a liquid are not rigidly held in place and are less closely packed than are the particles in a solid.
• This allows a liquid to flow and take the shape of its container, although it may not completely fill the container.
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LiquidsLiquids
• Because of the way the particles of a liquid are packed, liquids are virtually incompressible. Like solids, liquids tend to expand only slightly when heated.
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GasesGases• A gas is a form of matter that flows to conformto the shape of its container and fills the entirevolume of its container.
• Compared to solids and liquids, the particles of gases are very far apart.
• Because of the significant amount of space between particles, gases are easily compressed.
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PlasmaPlasma
�� Plasmas or ionized gases can exist at Plasmas or ionized gases can exist at
temperatures starting at several thousand temperatures starting at several thousand
degrees Celsius (degrees Celsius (°°C). C).
–– Two examples of plasma are the charged air Two examples of plasma are the charged air
produced by produced by lightninglightning, and a , and a starstar such as our such as our
own own sunsun..
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Physical Changes
• A substance often undergoes changes that result in a dramatically different appearance yet leave the composition of the substance unchanged.
• An example is the crumpling of a sheet of aluminum foil.
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Chemical ChangesChemical Changes
• Chemical properties relate to the ability of a substance to combine with or change into one or more substances.
• A process that involves one or more substances changing into NEW substances is called a chemical change, which is commonly referred to as a chemical reaction.
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Chemical ChangesChemical Changes
• The new substances formed in the reaction have different compositions and different propertiesfrom the substances present before the reaction occurred.
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Chemical ChangesChemical Changes
� Rust is a chemical combination of iron and oxygen.
� In chemical reactions, the starting substances are called reactants and the new substances that are formed are called products.
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Conservation of MassConservation of Mass
• By carefully measuring mass before and after many chemical reactions, it was observed that, although chemical changes occurred, the total mass involved in the reaction remained constant.
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Conservation of massConservation of mass
• The law of conservation of massstates that mass is neither created nor destroyed during a chemical reaction—it is conserved.
• The law of conservation of mass is one of the most fundamental concepts of chemistry.
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Conservation of MassConservation of Mass
• The equation form of the law of conservation of mass is:
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Review QuestionsReview Questions
� Identify each of the following as an example
� of a chemical change or a physical change.
�� Moisture in the air forms beads of water
� on a cold windowpane.
� An electric current changes water into
� hydrogen and oxygen.
� Yeast cells in bread dough make carbon
� dioxide an ethanol from sugar.
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Review QuestionsReview Questions
� A reaction between sodium hydroxide and hydrogen chloride gas produces sodium chloride and water. A reaction of 22.85 g of sodium hydroxide with 20.82 g of hydrogen chloride gives off 10.29 g of water. What mass of sodium chloride is formed in the reaction?